From having made a bunch of trips to Maui, I'd say your choice of South Maui is a good one. Kihei has a lot of restaurants, from the simple and inexpensive to some very nice higher-end places. The boat ride from Kihei to Molokini is short (I like Mike Severns best) and there are many secondary dive sites the operator can choose from for the second dive. Best of all, from my standpoint, there is excellent and very easy shore diving in South Maui. Frankly, many of the creatures people are excited to see in Molokini are just as easily found near shore. Turtles, morays, white tip reef sharks, and frogfish are within shore diving distance. Although my husband and I can afford boat diving, we've gotten to the point where we don't bother on some of our trips, and virtually never do more than one day on a boat. We have just as much fun from shore, and do it on our own schedule.
If you want to go and do the Cathedrals and pinnacles off Lanai, which are fun, taking a boat out of Lahaina is better than the long boat ride from Kihei. Depending on traffic and time of day, it's about a 45 minute drive up to Lahaina. (There's some great shore diving up there, too, including my favorite Maui dive.)
A lot of the shore diving sites have pretty easy parking and access, and some also have restrooms and showers. Ulua Beach is a good one, although one wants to get there fairly early in the morning, because the parking lot fills up. Makena Landing is another easy parking, easy access site.
But I don't know anywhere you can walk to boats or shore sites, unless you happen to be staying at the hotel near that particular beach. The drives aren't long, though.
If you want to go and do the Cathedrals and pinnacles off Lanai, which are fun, taking a boat out of Lahaina is better than the long boat ride from Kihei. Depending on traffic and time of day, it's about a 45 minute drive up to Lahaina. (There's some great shore diving up there, too, including my favorite Maui dive.)
A lot of the shore diving sites have pretty easy parking and access, and some also have restrooms and showers. Ulua Beach is a good one, although one wants to get there fairly early in the morning, because the parking lot fills up. Makena Landing is another easy parking, easy access site.
But I don't know anywhere you can walk to boats or shore sites, unless you happen to be staying at the hotel near that particular beach. The drives aren't long, though.